The present invention relates to aqueous dispersions of polymers obtained from the emulsion polymerization of a mixture of monomers, in which at least one of the monomers is. an unsaturated heterocycle. The invention also relates to the use of these aqueous polymer dispersions in crosslinking processes.
Coating compositions which crosslink at a temperature of above or equal to room temperature are known from the prior art. Some of these compositions result from reactions between latices separately comprising carboxylic ester functions and hydroxyl functions, or between latices comprising both hydroxyl functions and.carboxylic ester functions, particularly in the form of xcex2-hydroxy ester.
The reactions between the hydroxyl and carboxylic ester functions can be initiated and catalysed at room temperature with catalytic systems created in situ, after reacting a nucleophile such as, for example, an imidazole with an epoxide.
However, these compositions have a certain number of drawbacks.
The main problem is the stability on storage, also known as the xe2x80x9cpot lifexe2x80x9d, of mixtures containing the abovementioned latices and the catalytic system.
Specifically, the mixtures of latex and of catalytic system of the prior art have a pot life which is much too short to make them manipulable and economically interesting: the pot life is often less than or equal to 4 hours.
In addition, the use of the catalytic systems of the prior art can pose formulation problems: the nucleophilic compound is not always easy to disperse in the reaction medium, and more particularly in aqueous medium.
Moreover, although room-temperature crosslinking processes have already been described, the crosslinking is generally efficient only at temperatures above room temperature.
It has been observed, entirely surprisingly and unexpectedly, that by modifying certain parameters of the catalytic system, in particular the starting nucleophile, it is possible to overcome the drawbacks mentioned above.
Thus, the aim of the present invention is to propose a polymer based on an unsaturated nucleophilic heterocycle which, when mixed a latex, has an improved stability on storage (pot life) and good reactivity at the time of use.
Another aim of the invention is to propose a polymer based on an unsaturated nucleophilic heterocycle which does not pose any problems of dispersion in a given reaction medium.
Finally, another aim of the invention is to propose a polymer based on an unsaturated nucelophilic heterocycle which efficiently initiates and catalyses room-temperature crosslinking processes.
To this end, a subject of the invention is an aqueous dispersion of a water-insoluble polymer (I) obtained from the emulsion polymerization of a mixture of monomers comprising:
at least one unsaturated heterocyclic monomer (A),
and optionally at least one ethylenically unsaturated monomer (B).
A subject of the invention is also a process for crosslinking a latex (II) containing an epoxide function, using the dispersion of polymer (I).
The invention thus relates firstly to an aqueous dispersion of a water-insoluble polymer (I) obtained from the emulsion polymerization in water of a mixture of monomers comprising:
at least one unsaturated heterocyclic monomer (A):
comprising at least one nucleophilic hetero atom,
containing at least one exocyclic ethylenic unsaturation, and
whose heterocycle comprises at least one ethylenic unsaturation, and
optionally at least one ethylenically unsaturated monomer (B) containing a function chosen from (meth)acrylamides, carboxylic acids or carboxylic acid salts, carboxylic esters, organosulphuric acids or organosulphuric acid salts, sulphonic acids or sulphonic acid salts, phosphonic acids or phosphonic acid salts, vinyl esters and aromatic monomers containing at least one exocyclic ethylenic unsaturation.
In the context of the present invention, the term xe2x80x9cpolymerizationxe2x80x9d means either homopolymerization (polymerization of identical monomers) or copolymerization (polymerization of different monomers).
According to an essential characteristic of the invention, the polymer (I) is in the form of an aqueous dispersion. Such aqueous polymer disperions are commonly known as latices.
The polymer (I) is obtained from the emulsion polymerization of at least one monomer. (A) This monomer (A) comprises at least one nucleophilic hetero atom. The expression xe2x80x9cnucleophilic hetero atomxe2x80x9d means a trivalent hetero atom belonging to group VB of the Periodic Table of the Elements. Throughout the specification, the Periodic Table is that of the xe2x80x9csupplement to the Bulletin of the French Chemical Society, No. 1, January 1966xe2x80x9d. These hetero atoms may be nitrogen, phosphorus, arsenic, antimony or bismuth. The nucleophilic hetero atom is preferably nitrogen. The unsaturated heterocyclic monomers (A) preferably comprise at least nucleophilic hetero atoms, in particular two nitrogen atoms.
The monomer A should also contain an ethylenic unsaturation in its heterocycle and an exocyclic ethylenic unsaturation. At least one of the nucleophilic hetero atoms and/or at least one of the carbon atoms of the heterocycle may be substituted with a carbon-based chain containing at least two carbon atoms and at least one ethylenic unsaturation, it being possible for the carbon-based chain to be optionally functionalized. Substituents which may be mentioned as a guide are carbon-based chains, in particular vinyl, allyl, propenyl, butenyl and butadienyl, and functionalized carbon-based chains, in particular acrylate and methacrylate. In the monomer A, at least one of the carbon atoms of the unsaturated heterocycle can also be substituted with at least one linear or branched alkyl group containing 1 to 8 carbon atoms. In this respect, the linear or branched alkyl group can be methyl, ethyl, propyl, isopropyl or n-butyl.
The monomers (A) can belong to the imidazole, imidazoline, amidine or guanidine family. They preferably belong to the imidazole family. The monomer is more particularly N-vinylimidazole.
In the present invention, the polymer (I) can be a homopolymer obtained from the homopolymerization of a mixture composed exclusively of monomers (A), the monomers (A) being identical. The polymer (I) can also be a copolymer obtained from the copolymerization of a mixture of monomers (A) and (B).
The monomer B is ethylenically unsaturated and contains a function chosen from carboxylic acid or carboxylic acid salts, carboxylic esters, organosulphuric acids or organosulphuric acid salts, sulphonic acids or sulphonic acid salts, phosphonic acids or phosphonic acid salts, vinyl esters, (meth)acrylamides or aromatic monomers (B) containing at least one exocyclic ethylenic insaturation.
The ethylenically unsaturated monomer (B) may be chosen more particularly from:
carboxylic acids or carboxylic acid salts of the (meth)acrylic type, such as acrylic acid, methacrylic acid or sodium acrylate; dicarboxylic acids such as itaconic acid, maleic acid or fumaric acid; hemiesters thereof, such as the methyl, ethyl, propyl, n-butyl or isobutyl hemiesters; or salts thereof such as the sodium, potassium or ammonium salts thereof,
carboxylic esters of the acrylic type in which the alkyl group contains from 1 to 20 carbon atoms, such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, isopropyl acrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, decyl acrylate, decyl methacrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate or stearyl methacrylate,
organosulphuric acids or the alkali metal or alkaline-earth metal salts of organosulphuric acids, such as vinylsulphuric acid or vinylphenylsulphuric acid,
sulphonic acids or the alkali metal or alkaline-earth metal salts of sulphonic acids, for example vinylsulphonic acids such as vinylsulphonic acid, styrenesulphonic acid, 2-acrylamido-2-methylpropanesulphonic acid or sodium methallyl sulphonate,
phosphonic acids or the alkali metal or alkaline-earth metal salts of phosphonic acids, for example vinylphosphonic acid,
vinyl esters in which the portion comprising the ester function contains 1 to 7 carbon atoms, such as vinyl acetate, vinyl Versatate(copyright) or vinyl propionate,
(meth)acrylamides and derivatives thereof in which the alkyl group contains from 1 to 10 carbon atoms, such as acrylamide and methacrylamide, and
aromatic monomers containing at least one exocyclic ethylenic unsaturation and containing 8 to 18 carbon atoms, such as styrene, vinyltoluene or xcex1-methylstyrene.
The ethylenically unsaturated monomer (B) is preferably chosen from carboxylic esters of the (meth)acrylic type, in which the alkyl group contains from 1 to 20 carbon atoms, such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, isopropyl acrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, decyl acrylate, decyl methacrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate or stearyl methacrylate.
According to one preferred embodiment, the mixture of monomer(s) (B) comprises few or no (meth)acrylamides and/or carboxylic acids, since these monomers have the property of making the polymer (I) water-soluble. Thus, the amount of (meth)acrylamides or of carboxylic acids used should preferably be fairly small so as to avoid making the polymer (I) soluble.
According to the preferred embodiment, the aqueous dispersion of polymer (I) is obtained from the copolymerization of a mixture of monomers comprising:
N-vinylimidazole as monomer (A), and
methyl methacrylate and/or n-butyl acrylate as monomer (B).
The content of monomer(s) (A) is generally between 1% and 100% by weight, preferably between 1% and 20% by weight and more particularly between 1% and 6% by weight, relative to the total weight of the polymer (I).
If monomers (B) are used to synthesise the polymer (I), the content of monomer(s) (B) is generally between 1% and 99% by weight, preferably between 80% and 99% by weight and more particularly between 94% and 99% by weight, relative to the total weight of the polymer (I).
The polymer (I) can be made more reactive by adding a third type of monomer to the polymerization mixture. The reason for this is that the polymer (I) can be obtained from the copolymerization of a mixture of monomers. (A), (B) and of at least one. hydroxycarboxylic ester (C) chosen from acrylic and methacrylic esters in which the hydroxyalkyl group contains from 2 to 10 carbon atoms. The carboxylic esters (C) can be chosen from 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl acrylate and 4-hydroxybutyl methacrylate. The content of monomer(s) (C) is generally between 1% and 40% by weight and preferably between 1% and 30% by weight relative to the total weight of the polymer (I).
The aqueous dispersion of polymer (I) according to the invention is obtained by simple mixing of monomers (A), optionally (B) and/or (C), followed by emulsion polymerization in water. It is important for the emulsion to be prepared in water since the use of solvents generally results in precipitation of the polymer (I); the polymer (I) is thus not in the form of latex. The monomers used can be introduced as a mixture or separately and simultaneously into the reaction medium, either before the start of the polymerization in a single portion, or during the polymerization in successive fractions or continuously. It is generally preferable for the emulsion polymerization to be carried out at a pH of at least 7, or even of at least 8. Consequently, the pH of the aqueous dispersion of polymer. (I) according to the invention preferably has a pH of at least 7, or even of at least 8. The polymerization is usually carried out in the presence of an emulsifier and a polymerization initiator. Emulsifiers which can generally be used are the conventional anionic agents represented in particular by fatty acid salts, alkyl sulphates, alkyl sulphonates, alkylaryl sulphates, alkylaryl sulphonates, aryl sulphates, aryl sulphonates, sulphosuccinates and alkyl phosphates of alkali metals, and hydrogenated or non-hydrogenated abietic acid salts. They are generally used in a proportion of from 0.01% to 5% by weight relative to the total weight of the monomers. The emulsion-polymerization initiator is represented more particularly by hydroperoxides such as aqueous hydrogen peroxide solution, cumene hydroperoxide, diisopropylbenzene hydroperoxide, paramenthane hydroperoxide and tert-butyl hydroperoxide, and by persulphates such as sodium persulphate, potassium persulphate and ammonium persulphate. It is used in an amount of between 0.05% and 2% by weight relative to the total weight of the monomers. These initiators are optionally combined with a reducing agent, such as sodium bisulphite or sodium formaldehydesulphoxylate, polyethyleneamines, sugars (dextrose, sucrose) and metal salts. The amount of reducing agent used ranges from 0% to 3% by weight relative to the total weight of the monomers. The reaction temperature, which depends on the initiator used, is generally between 0xc2x0C. and 100xc2x0 C. and preferably between 30xc2x0 C. and 90xc2x0 C. A transfer agent can be used, in proportions ranging from 0% to 3% by weight relative to the monomer(s) and is generally chosen from mercaptans such as N-dodecyl mercaptan and tert-dodecyl mercaptan, cyclohexene and halogenated hydrocarbons such as chloroform, bromoform or carbon tetrachloride. This transfer agent allows the length of the molecular chains to be controlled. It is added to the reaction medium either before the polymerization or during polymerization.
Another subject of the present invention is the use of the aqueous dispersions of polymer (I) described above in crosslinking processes.
Thus, the invention relates to a process for crosslinking a latex (II) prepared from a mixture:
of at least one monomer containing ethylenic unsaturation (D), and
either of at least one ethylenically unsaturated monomer containing an epoxide function (E), or of at least one polymer containing an epoxide function (EP), or of a mixture of monomers (E) and of polymers (EP), in which the said latex (II) is reacted with an aqueous dispersion of polymer (I) as defined above.
The monomers containing ethylenic unsaturation (D) can be chosen from:
aromatic monomers containing at least one exocyclic ethylenic unsaturation, such as styrene, xcex1-methylstyrene, alkylstyrenes such as methylstyrene, halostyrenes such as chlorostyrene, vinyltoluene, vinylnaphthalene, divinylbenzene, diallyl phthalate, or
monomers containing a carboxylic ester function such as acrylic and methacrylic esters in which the alkyl group is C1 to C18, optionally substituted copolymerizable xcex2-ketocarboxylic esters, and vinyl esters such as vinyl acetate, vinyl Versatate(copyright) or vinyl propionate. Among the acrylic and methacrylic esters whose alkyl group is C1 to C18, mention may be made in particular of methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, cyclohexyl acrylate, cyclohexyl methylacrylate, decyl acrylate, decyl methacrylate, isodecyl acrylate, isodecyl methacrylate, stearyl acrylate or stearyl methacrylate. Preferred examples of this monomer are styrene and alkylstyrenes. Among the xcex2-ketocarboxylic esters which may be mentioned are vinyl acetoacetate, allyl acetoacetate, acetoacetoxyethyl methacrylate and acetoacetoxyethyl acrylate.
In this type of crosslinking process, the presence of an epoxide function in the medium is essential. The monomers (E) can be chosen from glycidyl acrylate, glycidyl methacrylate and allyl glycidyl ether. The polymers containing an epoxide function (EP) can be chosen from bisphenol A diglycidyl ether, diglycidyl adipate, 1,4-diglycidyl butyl ether and derivatives thereof. In the context of the present invention, a latex (II) consisting exclusively of at least one polymer containing an epoxide function (EP) may also be envisaged.
It is preferable for the polymer (I) to be obtained from the polymerization of a mixture of monomer(s) (B) comprising few or no carboxylic acids since these can limit the crosslinking reaction with the latex (II). Thus, according to a preferred embodiment, the crosslinking process takes place in the presence of an aqueous dispersion of polymer (I) obtained from the copolymerization of a mixture of monomers comprising:
N-vinylimidazole as monomer (A), and
methyl methacrylate and/or n-butyl acrylate as monomer (B).
A first embodiment consists in crosslinking a latex (II) prepared from a mixture of at least one monomer containing ethylenic unsaturation (D) and of at least one ethylenically unsaturated monomer containing an epoxide function (E).
A second embodiment consists in crosslinking a latex (II) prepared from a mixture of at least one monomer containing ethylenic unsaturation (D) and of at least one polymer containing an epoxide function (EP).
A third embodiment consists in crosslinking a latex (II) prepared from a mixture of at least one monomer containing ethylenic unsaturation (D) and of at least one ethylenically unsaturated monomer containing an epoxide function (E) mixed with at least one polymer containing an epoxide function (EP).
A fourth embodiment consists in crosslinking a latex (II) prepared from at least one ethylenically unsaturated monomer containing an epoxide function (E) and a mixture of monomers containing ethylenic unsaturation (D) comprising at least one aromatic monomer containing an exocyclic ethylenic unsaturation and at least one (meth)acrylic ester.
A fifth embodiment consists in crosslinking a latex (II) prepared from at least one ethylenically unsaturated monomer containing an epoxide function (E) and a mixture of monomers containing ethylenic unsaturation (D) comprising at least one aromatic monomer containing an exocyclic ethylenic unsaturation and at least one xcex2-ketocarboxylic ester.
The crosslinking process according to the invention can lead to dense crosslinked networks. When such networks are desired, the latex (II) is generally prepared from a mixture also comprising at least one ethylenically unsaturated monomer containing a hydroxyl function (F). The monomers (F) can be chosen from 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl acrylate and 4-hydroxybutyl methacrylate. This monomer is preferably 2-hydroxyethyl acrylate or 2-hydroxyethyl methacrylate.
A sixth embodiment consists in crosslinking a latex (II) prepared from a mixture of monomers containing ethylenic unsaturation (D) comprising at least one aromatic monomer containing an exocyclic ethylenic unsaturation and at least one (meth)acrylic ester, at least one ethylenically unsaturated monomer containing an epoxide function (E) and at least one ethylenically unsaturated monomer containing a hydroxyl function (F).
A seventh embodiment consists in crosslinking a latex (II) prepared from a mixture of monomers containing ethylenic unsaturation (D) comprising at least one aromatic monomer containing an exocyclic ethylenic unsaturation and at least one (meth)acrylic ester, at least one ethylenically unsaturated monomer containing an epoxide function (E) mixed with at least one polymer containing an epoxide function (EP) and at least one ethylenically unsaturated monomer containing a hydroxyl function (F).
An eighth embodiment consists in crosslinking a latex (II) consisting exclusively of polymers containing an epoxide function (EP), for example bisphenol A diglycidyl ether, diglycidyl adipate or 1,4-diglycidyl butyl ether. In this case, the crosslinking process is generally carried out with a dispersion of polymer (I) obtained from the homopolymerization of a mixture consisting exclusively of monomers (A).
The crosslinking process according to the invention can take place in the presence of a compound (G) capable of reacting according to the Michael reaction. The compound (G) can be chosen from resins comprising at least two double bonds conjugated with at least one carbonyl function (Cxe2x95x90O), in particular 1,1,1-tris(hydroxymethyl)-propane-tri-acrylate.
The latex (II) and the polymer (I) are generally mixed in proportions such that the epoxide function/nucleophilic function ratio is equimolar.
The crosslinking process can be carried out in the presence of common adjuvants such as thickeners, wetting agents, antifoams, glycols, coalescers, pigments, dispersants and base activators. Depending on the intended application, the amount of adjuvant(s) used may vary. A person skilled in the art knows how to select the appropriate amounts depending on the intended application.
The aqueous dispersions of polymers (I) and latex (II) can crosslink at room temperature or at higher temperature to form thermoset coatings and films, in particular when it is desired to produce coatings such as varnishes and paints.
The aqueous dispersions of polymers (I) and latex (II) preferably crosslink at room temperature to form films and coatings. The expression xe2x80x9croom temperaturexe2x80x9d means a temperature between 15xc2x0 C. and 30xc2x0 C. The aqueous dispersions of polymers (I) and latex (II) can also crosslink at lower temperatures to form films and coatings, for example at about 5xc2x0 C., if coalescers are incorporated.
These coatings can be applied to any type of substrate: wood, metal, concrete, plaster, terracotta, stones, bricks, tiles, plastics, glass, paper, leather and similar materials.
Finally, a subject of the invention is the product containing an aqueous dispersion of polymer (I), and a latex (II) prepared from a mixture of at least one monomer containing ethylenic unsaturation (D), at least one ethylenically unsaturated monomer containing an epoxide function (E) and optionally at least one polymer containing an epoxide function (EP), as a combination product for combined use for the preparation of a coating.
The expression xe2x80x9ccombined usexe2x80x9d means a use of the aqueous dispersion of polymer (I) and of the latex (II) together to obtain a coating; the dispersion of polymer (I) and of the latex (II) possibly being introduced simultaneously or separately.